This invention relates generally to dryer systems, and, more particularly, to control systems for clothes dryers.
An appliance for drying articles such as a clothes dryer for drying clothing articles typically includes a cabinet including a rotating drum for tumbling clothes and laundry articles therein. One or more heating elements heats air prior to air entering the drum, and the warm air is circulated through the air as the clothes are tumbled to remove moisture from laundry articles in the drum. See, for example, U.S. Pat. No. 6,141,887.
In an electric clothes dryer, a current is caused to flow in one or more electrical heaters to heat air introduced to the drum with a fan. A resistance value of the heater is based upon the desired capacity of the heater, and the heater is rated to operate at a predetermined voltage (e.g., 240 Volts AC). The input voltage to the heater, however, fluctuates over time. A voltage of a power source line may, for example, fluctuate up to 10%, of the rated value thereof. When the actual input voltage to the dryer is above the rated voltage (referred to herein as an over-voltage condition), current flowing through the heater is accordingly increased. In some cases, the current drawn by the heaters in an over-voltage condition can cause household circuit breakers to trip, thereby opening the circuit through the dryer. Tripping of circuit breakers due to dryer operation is both an impediment to dryer operation and a great inconvenience to dryer users who must reset the circuit breaker.
At least one known electric dryer system includes a control circuit apparatus including a switching device for opening and closing an electrical connection between a power source and a heater in an over-voltage condition to prevent overheating of the dyer and associated damage to machine components and clothing articles. The control circuit includes a comparator that produces an over-voltage signal corresponding to a difference between the supply voltage and a predetermined reference voltage corresponding to the heater rating. A pulse width of the over-voltage signal is counted, and a time value of the period to open the heater circuit is calculated by scaling a target pulse width by one of a plurality of experimentally determined constants α read from a table in a memory. Each constant a corresponds to the counted pulse width of the over-voltage signal, and the constants are selected to scale the target pulse width to maintain heater power consumption per unit time at the same level as if the heater operated at the rated voltage. See U.S. Pat. No. 4,469,654.
Unfortunately, the constants applicable to one machine are not necessarily applicable to another machine with different components. Therefore, constants must experimentally determined for each different machine. It would be desirable to provide a universal over-voltage control for a clothes dryer applicable across a variety of clothes dryer platforms.